Effect of heat treatment on filiform corrosion of aluminium alloy AA3005

The effect of heat treatment on the filiform corrosion (FFQ susceptibility of rolled aluminium alloy AA3005 at temperatures in the range 150-500 degre esC is investigated. A drastic loss of corrosion resistance takes place as a result of annealing at temperatures in excess of 350 degreesC. TEM invest igations revealed a highly deformed near-surface region, approximately 1 mu m thick, on the as-received material. The presence of this surface layer is caused by shear deformation of the surface region during rolling. The enha nced deformation undergone by the surface layer promotes secondary intermet allic precipitation in this region during subsequent heat treatment. The re sulting microstructure, where the near-surface region contains a higher den sity of fine intermetallic particles and lower solid solution levels of the more noble alloying elements than the underlying bulk, results in preferen tial attack of this layer during corrosion processes and is identified as t he main cause of the observed loss of FFC resistance. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.